Turmeric or “yellow root” is a general term for plants and plant materials having a high content of curcuminoids, compounds that have a strong colouring effect and which are used extensively in the colouring of e.g. food products. Turmeric plants belong to rhizomatous Curcuma species and have been known for centuries for their flavouring and colouring properties. The plants are grown commercially, particularly in India, but also in Bangladesh, China, Sri Lanka, Indonesia, Taiwan, Haiti, Jamaica and Peru.
It has been found that Curcuma plant materials contain three different curcuminoid compounds including, as the predominant colouring compound, curcumin having a strong yellow colour, and minor yellow and brownish-red components, i.e. the term “curcuminoids” includes curcumin (C), reddish orange and with two methoxy groups; demothoxy curcumin (DMC), orange-yellow with one methoxy group and bis-demothoxy curcumin (BDMC), yellow and without a methoxy group. The relative proportions of these three curcuminoid components in the source plant material, in particular in the rhizomes, have been reported by several groups. Thus, Perotti (1975) found a ratio of 60:30:10, Krishnamurthy et al. (1976) one of 49:29:22 and Govindaraian (1980) found a ratio of 42:24:34.
The Curcuma rhizomes, including the primary or mother rhizomes and several long cylindrical multi-branced secondary rhizomes growing downward from the primary rhizomes, that contain the curcuminoid compounds in an oily cell phase, are harvested at maturity, typically 8 to 9 months after planting.
After harvest, the rhizomes are cured in a process essentially comprising cooking the fresh rhizomes in water. This cooking step aids in producing a product of fairly uniform colour due to the diffusion of the yellow pigments from the individual oil containing cells into the surrounding tissues. After cooking, the material is spread and allowed to dry in the sun. When properly dried, the rhizomes become hard, almost horny and brittle, and of uniform yellow colour. This cured and dried turmeric product is marketed as bulbs and fingers, each type in polished and unpolished forms. This turmeric raw material is then made available to bulk purchase as a starting material for further processing resulting in commercial colouring agents.
Preparing more or less purified solvent extracts of Curcuma plant materials, in particular rhizomes as described above, provides commercial curcuminoid-containing colouring agents or compositions. Traditionally, methods for the isolation of curcuminoid colours from the Curcuma starting material involve conventional extraction methods typically using solvents of defined purity allowed by national and international food laws for the processing of food additives, and optionally further purification step(s).
The curcuminoid-containing phase that is obtained by the above extraction methods is in the form of an oleoresin comprising an essential oil containing the curcuminoids. The curcuminoid content of the oleoresin is typically in the range of 30-50% by weight. However, the essential oil fraction of the oleoresin has a very strong and bitter flavour, which for many purposes, such as colouring of food products, is undesirable. In order to meet the increasing demand for a highly concentrated flavour-free curcuminoid product, the oleoresin may be processed further. Thus, the oleoresin may subsequently be subjected to a crystallisation step resulting in the obtainment of a curcuminoid powder of a relatively high purity (typically >90% by weight) in respect of curcuminoids. The maximum yield of curcuminoids that can be obtained in this conventional process including the crystallisation step is about 60% by weight, i.e. only about 60% of the curcuminoids initially present in the oleoresin starting material is recovered in the crystal-containing powder.
The residual material that remains after the above separation of curcuminoid crystals consists mainly of the essential oil fraction of the oleoresin and a relatively high proportion of the curcuminoids initially present in the oleoresin, i.e. 40% by weight or more. However, this residual material, although it has a content of curcuminoids that confers to the residual material a yellowish colour, is unsuitable as a colouring agent, not only due to the extensive undesirable flavour, but also due to its relatively low colouring effect. Furthermore, the residual material as such is not directly applicable in e.g. food products. Presently, this residual material is, for these reasons, not utilised commercially and it therefore represents a substantial waste of curcuminoid colouring material. Evidently, this waste of curcumoids in the conventional process for providing concentrated and flavour-free curminoid (or “turmeric”) colouring agents or compositions adds significantly to the costs of providing such highly desirable products.
A strong industrial need therefore exists to render processes for providing such useful, and/or pure and concentrated high quality curcuminoid products economically feasible. This has been achieved by the present invention which is based on the discovery that the curcuminoid-containing waste material can be utilised as a starting material for commercially valuable novel curcuminoid colouring agents having excellent and particular colouring properties and, relative to commercial oleoresin products, a similar or even reduced content of undesired flavouring compounds.